The invention relates to an apparatus for measuring the positions and movements of the lower jaw relative to the upper jaw comprising a first holder to be secured in a fixed relationship to the upper jaw to the patient's head, a second holder to be secured to the lower jaw and a plurality of distance measuring means including a respective transmitter and receiver which are provided at the holders to determine the positions of the holders relative to each other.
In a known device of this type (EP laid open publication No. 0 025 201), the holders are jaw plates which are provided in the patient's mouth. The jaw plate of the upper jaw includes one sole transmitter, while a plurality of receivers are distributed at the jaw plate of the lower jaw, each receiver forming with the transmitter a distance measuring means. If the patient moves his lower jaw, the changing distances between each receiver and the transmitter are recorded. In an articulator containing the models of the lower and upper jaws, the jaw movements may be reproduced under control by the recorded data. With the use of three distance measurements, it is not possible, by means of the known system, to clearly identify all jaw movements. While due to the design of the measuring system, the jaw movements may be reproduced in an articulator, no exact measuring of the jaw and mouth movements is possible for all that. Above all, it is impossible to determine and check at the patient's head the articulation axis between lower and upper jaw whose position constantly changes during masticating movements.
It is the object of the invention to provide an apparatus of the foregoing type which allows to exactly cover and analyse the movements of the lower jaw relative to the upper jaw by clearly considering all of the degrees of freedom of the system.